Tense exchanges inside the Seoul Central District Court featured the first hearing of the criminal trial of former South Korean president Yoon Suk-yeol on Monday amid insurrection charges following his short-lived martial law declaration in December.

The prosecution presented a summary of its charges during the trial, while Yoon, a former top prosecutor, refuted them one by one and stressed that the martial law only lasted for a few hours, according to Yonhap News Agency.

"It goes against legal principles to build an insurrection case based on an indictment that looks like a printout of an incident that lasted only a few hours and was lifted immediately in a nonviolent manner upon accepting the National Assembly's demand to lift it," said Yoon, who has become the 5th former South Korean president to stand criminal trial.

Yoon said that, even during the initial investigation process, many statements included in the indictment — by people questioned — were made out of fear and guided by the investigation agency without verification.

He was formally removed from office over his martial law declaration after the Constitutional Court upheld on April 4 his impeachment. A snap presidential election is set for June 3.

Yoon's martial law attempt lasted about six hours from 10:27 pm on Dec 3 when he made the surprise announcement in a televised address. The National Assembly voted against it at 1:02 am on Dec 4 and Yoon formally lifted the martial law about three hours later.

The prosecution said Yoon led riots with the purpose of disrupting the country's constitution by mobilizing troops and police to areas including the National Assembly, the headquarters of the main opposition Democratic Party, and the National Election Commission.

Supporters gathered outside the court holding banners such as "Yoon Again" while his opponents held a news conference calling for his rearrest.

Meanwhile, on Monday, the ruling People Power Party, or PPP, began registration for candidates for the upcoming election.

Several key figures are expected to participate in the party's primary, including former labor minister Kim Moon-soo, former Daegu mayor Hong Joon-pyo, former PPP chairman Han Donghoon, and PPP lawmaker Anh Cheol-soo.

Seoul Mayor Oh Se-hoon, who had been seen as one of the leading presidential contenders for the party, said he will not participate in the primary.

Acting President and Prime Minister Han Duck-soo has remained silent on speculation that he may run for president.

The PPP will confirm its standard-bearer on May 3.

The liberal Democratic Party, or DP, also started receiving candidate registrations on the same day. But the party has decided there will be no open primary and the candidate will be selected by combining voting by party members and public opinion polls resulting in a 50:50 ratio. The final candidate will be confirmed on April 27.

Former DP leader Lee Jaemyung is a front-runner in opinion polls, maintaining a solid lead of 48.8 percent as a preferred presidential candidate in a weekly poll released on Monday by Realmeter.

Lee announced last week his policy road map if he becomes president, saying that he would focus on overcoming the national crisis in politics and economy.

Former labor minister Kim Moon-soo came next with 10.9 percent, followed by 8.6 percent for Han, the acting president.

As for party approval ratings, DP gained 46.7 percent, up 1.9 percentage points from the previous week. PPP had 33.1 percent, down 2.6 percentage points.

Economic instability

"The political turmoil from an early election triggered by the impeachment of former president Yoon Suk-yeol, combined with worsening external economic situation due to US tariffs, has heightened economic instability," Realmeter said in its report.

This has increased public anxiety, fueling dissatisfaction with the government and the ruling party, which resulted in a negative impact on PPP's approval ratings, it said.

Yoon's next hearing is scheduled for April 21, with experts saying the trial is likely to be a lengthy one.

"The first verdict is likely to be delivered around August, but the case involves around 70,000 pages of evidence and numerous witnesses. So if deemed necessary by the court, the trial may be extended," lawyer Min Kyoung-sic told AFP.

Agencies contributed to this story.

kelly@chinadailyapac.com